1. Field of the Invention
The present invention relates to a system, method, and program for shadowing data at a remote site and, in particular, shadowing data in an open systems environment.
2. Description of the Related Art
Data storage systems often include a data protection component that involves creating a back-up copy of data to use in the event of a system failure. One such data protection system involves the use of a computer at a remote site, often referred to as the secondary system, shadowing data storage at a primary site having a primary computer and storage. If there is a system failure at the primary site, then the data can be recovered from the secondary site. One such disaster recovery system that provides data shadowing is the International Business Machines Corporation (IBM) Peer-to-Peer Remote Copy (PPRC) system. In a PPRC system, a primary storage controller provides access to a primary mass storage systems, such as one or more Direct Access Storage Devices (DASDs), comprised of interconnected hard disk drives. The storage controller manages the flow of data from host systems to DASDs. A secondary controller provides a shadow copy of designated volumes in the primary DASD in a secondary mass storage system. A high speed dedicated line, such as Enterprise System Connection (ESCON) channels **, may be used to transfer data from the primary controller to the secondary controller. In PPRC systems, a relationship is established between volumes in the primary DASD and the secondary DASD by copying the designated volumes from the primary DASD to the secondary DASD through the primary and secondary controllers. After the establishment phase, any updates to the protected volumes in the primary DASD are copied over to the secondary controller and DASD to synchronize the data therebetween.
**Enterprise Storage Server and ESCON are registered trademarks and Fibre Channel Raid Storage Controller is a trademark of IBM; Windows and Windows NT are registered trademarks of Microsoft Corporation. 
Current data shadowing systems require that both the primary and secondary control unit include special purpose data shadowing firmware or software to implement the data shadowing relationship between a primary and secondary controllers, such as the IBM PPRC and XRC software and firmware. In such systems, typically, the controllers involved in shadowing customer data are from the same vendor.
Many computer networks operate in an open system environment and transfer data using the Small Computer System Interface (SCSI) or Fibre Channel architectures. In an open system environment, systems may be from different vendors and would not communicate using special, vendor specific protocols, such as PPRC or XRC. Thus, there is a need to provide data shadowing in an open systems environment where the systems do not include special purpose firmware or software to implement such data shadowing.
To overcome the limitations in the prior art described above, preferred embodiments disclose a method, system, and program for providing a shadow copy of data storage areas in a primary site to data storage areas in a secondary site. A definition is made of storage areas in the primary site having data to be shadowed and corresponding storage areas in the secondary site to shadow data at the storage areas in the primary site. A shadow pair comprises one primary storage area and one secondary storage area that shadows data for the primary storage area in the pair. A standard data transfer interface protocol command, such as a SCSI or Fibre Channel command, is used to configure status storage areas in the secondary site to provide status information and data for each primary and secondary storage area. A write command in the standard data transfer interface protocol is then used to write status information to the status storage areas indicating status of the shadowed data at the secondary storage areas in the pairs.
In further embodiments, an update from a host to one storage area in the primary site in one shadow pair to update is received. The write command in the standard data transfer interface protocol is then used to write the update to the storage area for the pair to update.
Preferred embodiments provide a methodology for allowing a remote controller in an open systems environment to function as a secondary site to shadow data at a primary site. Preferred embodiments allow the primary controller to use a standard data transfer interface protocol, such as SCSI or Fibre Channel Protocol (FCP), to place status information and data at the secondary site on the state of data being shadowed. In the event of a failure at the primary site, another system can use the status information to determine the consistency of the data at the secondary site in shadowing the data at the primary site. With the preferred embodiments, the secondary controller does not include special purpose data shadowing because the primary controller uses standard data transfer protocols to maintain data shadowing status at the secondary site.